Cygwin: ssh login issue if client have a keyfile - ssh

Question

I have an issue with Cygwin on one windows server (2008 R2 STD)
it's a first time a saw that:
First, I saw a little bug after the installation of cygwin, when I open a Cygwin terminal the username have the hostname in the name (WANCYFILE3 is the hostname):
WANCYFILE3+BoMBkpAccount#WANCYFILE3 ~
$
and when i create a /etc/passwd with mkpasswd i have the same issue:
WANCYFILE3+BoMBkpAccount#WANCYFILE3 ~
$ mkpasswd
SYSTEM:*:18:18:U-NT AUTHORITY\SYSTEM,S-1-5-18:/home/SYSTEM:/bin/bash
LOCAL SERVICE:*:19:19:U-NT AUTHORITY\LOCAL SERVICE,S-1-5-19:/:/sbin/nologin
NETWORK SERVICE:*:20:20:U-NT AUTHORITY\NETWORK SERVICE,S-1-5-20:/:/sbin/nologin
Administrators:*:544:544:U-BUILTIN\Administrators,S-1-5-32-544:/:/sbin/nologin
NT SERVICE+TrustedInstaller:*:328384:328384:U-NT SERVICE\TrustedInstaller,S-1-5-80-956008885-3418522649-1831038044-1853292631-2271478464:/:/sbin/nologin
WANCYFILE3+Administrator:*:197108:197121:U-WANCYFILE3\Administrator,S-1-5-21-1686359761-1676169977-233769372-500:/home/Administrator:/bin/bash
WANCYFILE3+BoMBkpAccount:*:197608:197121:U-WANCYFILE3\BoMBkpAccount,S-1-5-21-1686359761-1676169977-233769372-1000:/home/BoMBkpAccount:/bin/bash
WANCYFILE3+cyg_server:*:197613:197121:U-WANCYFILE3\cyg_server,S-1-5-21-1686359761-1676169977-233769372-1005:/home/cyg_server:/bin/bash
WANCYFILE3+Guest:*:197109:197121:U-WANCYFILE3\Guest,S-1-5-21-1686359761-1676169977-233769372-501:/home/Guest:/bin/bash
WANCYFILE3+sshd:*:197612:197121:U-WANCYFILE3\sshd,S-1-5-21-1686359761-1676169977-233769372-1004:/home/sshd:/bin/bash
for information the home directory is good:
WANCYFILE3+BoMBkpAccount#WANCYFILE3 ~
$ pwd
/home/BoMBkpAccount
now during the installation on ssh with the command "ssh-host-config"
i needed to replace the creation of the automatic user "WANCYFILE3+cyg_server" with "cyg_server"
*** Info: The following privileged accounts were found: 'WANCYFILE3+cyg_server' .
*** Info: This script plans to use 'WANCYFILE3+cyg_server'.
*** Info: 'WANCYFILE3+cyg_server' will only be used by registered services.
*** Query: Do you want to use a different name? (yes/no) yes
*** Query: Enter the new user name: cyg_server
*** Query: Reenter: cyg_server
otherwise i have this issue:
*** Info: This script plans to use 'WANCYFILE3+cyg_server'.
*** Info: 'WANCYFILE3+cyg_server' will only be used by registered services.
*** Query: Please enter the password for user 'WANCYFILE3+cyg_server':
*** Query: Reenter:
/usr/bin/cygrunsrv: Error installing a service: CreateService: Win32 error 1057:
The account name is invalid or does not exist, or the password is invalid for the account
*** ERROR: Installing sshd as a service failed!
now the sshd service work with the password:
WANCYFILE3+BoMBkpAccount#WANCYFILE3 ~/.ssh
$ ssh localhost
WANCYFILE3+BoMBkpAccount#localhost's password:
Last login: Tue Apr 21 10:45:46 2015 from ::1
WANCYFILE3+BoMBkpAccount#WANCYFILE3 ~
$
but not if the client have a keyfile:
WANCYFILE3+BoMBkpAccount#WANCYFILE3 ~
$ ssh-keygen.exe
Generating public/private rsa key pair.
....
WANCYFILE3+BoMBkpAccount#WANCYFILE3 ~
$ ssh localhost
Connection closed by ::1
i tryed to add the publickey in the authorized_keys but it's a same issue
for exemple from a another ssh client:
$ ssh-copy-id -i ./backupkey_BOM_Ancy.pub WANCYFILE3+BoMBkpAccount#WANCYFILE3.ancy.societe.com
WANCYFILE3+BoMBkpAccount#wancyfile3.ancy.societe.com's password:
Now try logging into the machine, with "ssh 'WANCYFILE3+BoMBkpAccount#WANCYFILE3.ancy.societe.com'", and check in:
.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.
$ ssh -i ./backupkey_BOM_Ancy WANCYFILE3+BoMBkpAccount#WANCYFILE3.ancy.societe.com
Connection closed by 10.131.16.34
whith verbose connexion:
$ ssh -v -i ./backupkey_BOM_Ancy WANCYFILE3+BoMBkpAccount#WANCYFILE3.ancy.societe.com
OpenSSH_5.5p1 Debian-6+squeeze3, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to WANCYFILE3.ancy.societe.com [10.131.16.34] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file ./backupkey_BOM_Ancy type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file ./backupkey_BOM_Ancy-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.8
debug1: match: OpenSSH_6.8 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-sha1 none
debug1: kex: client->server aes128-ctr hmac-sha1 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<2048<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'wancyfile3.ancy.societe.com' is known and matches the RSA host key.
debug1: Found key in /root/.ssh/known_hosts:62
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Offering public key: ./backupkey_BOM_Ancy
Connection closed by 10.131.16.34
$
After 3 installations of cygwin, I can't find this issue.
do you have any idea?
Thanks for your help (and sorry for my English)

Answer 1

debug1: Offering public key: ./backupkey_BOM_Ancy
Connection closed by 10.131.16.34
$
You need to figure out why the server is closing the connection on you. If this were a unix system, I'd say to check the system logs (usually one of the files in /var/log) for messages from sshd. I don't know what the cygwin equivalent of that is.
My guess is that you're authenticating, and the server is trying to start a login session for you. But the program that it's trying to start as your shell is missing, malfunctioning, or it's exiting as soon as it has started.